scholarly journals Uncovering the dynamic fracture behavior of PMMA

2019 ◽  
Author(s):  
Javad Mehrmashhadi ◽  
Longzhen Wang ◽  
Florin Bobaru
Keyword(s):  
Crack Propagation ◽  
Dynamic Fracture ◽  
Fracture Behavior ◽  
Numerical Models ◽  
Process Zone ◽  
Crack Tip ◽  
Dynamic Crack Propagation ◽  
Experimental Investigations ◽  
Dynamic Crack ◽  
Strain Rates

Experimental investigations of dynamic crack propagation in PMMA induced by impact show single cracks running at around 300-400 m/s. Existing numerical models for simulating dynamic fracture in PMMA consistently produce crack propagation speeds significantly higher than those measured experimentally. Here we uncover the reason for this puzzle by showing that localized softening in the fracture process zone (caused by heating due to high strain rates in front of the crack tip), leads to crack propagation speeds that match the observed ones. We introduce a new constitutive model in our peridynamic formulation for PMMA to account for material softening in the crack tip region. With the new model, the computed crack speed and crack length evolution match very closely those found experimentally.

scholarly journals Micro-mechanical Insights Into the Dynamics of Crack Propagation in Snow Fracture Experiments

2021 ◽  
Author(s):  
Grégoire Bobillier ◽  
Bastian Bergfeld ◽  
Jürg Dual ◽  
Johan Gaume ◽  
Alec Herwijnen ◽  
...  
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Field Experiments ◽  
Process Zone ◽  
Crack Tip ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Stress Concentrations ◽  
Weak Layer ◽  
Mountainous Regions

Abstract Dry-snow slab avalanches result from the propagation of compacting shear bands in highly porous weak layers buried within a stratified and metastable snowpack. While our understanding of slab avalanche mechanisms improved with recent experimental and numerical advances, fundamental micro-mechanical processes remain poorly understood due to a lack of non-invasive monitoring techniques. Using a novel discrete micro-mechanical model, we reproduced crack propagation dynamics observed in field experiments, which employ the propagation saw test. The detailed microscopic analysis of weak layer stresses and bond breaking allowed us to define the crack tip location of closing crack faces, analyze its spatio-temporal characteristics and monitor the evolution of stress concentrations and the fracture process zone both in transient and steady-state regimes. Results highlight the occurrence of a steady state in crack speed and stress conditions for sufficiently long distances of crack propagation (> 4 m). Crack propagation without external driving shear force is possible due to the local mixed-mode shear-compression stress nature at the crack tip induced by slab bending and weak layer volumetric collapse. Our result shed light into the microscopic origin of dynamic crack propagation in snow slab avalanche release that eventually will improve the evaluation of avalanche release sizes and thus hazard management and forecasting in mountainous regions.

scholarly journals Micro-mechanical insights into the dynamics of crack propagation in snow fracture experiments

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Grégoire Bobillier ◽  
Bastian Bergfeld ◽  
Jürg Dual ◽  
Johan Gaume ◽  
Alec van Herwijnen ◽  
...  
Keyword(s):  
Steady State ◽  
Crack Propagation ◽  
Field Experiments ◽  
Process Zone ◽  
Crack Tip ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Stress Concentrations ◽  
Weak Layer ◽  
Mountainous Regions

AbstractDry-snow slab avalanches result from crack propagation in a highly porous weak layer buried within a stratified and metastable snowpack. While our understanding of slab avalanche mechanisms improved with recent experimental and numerical advances, fundamental micro-mechanical processes remain poorly understood due to a lack of non-invasive monitoring techniques. Using a novel discrete micro-mechanical model, we reproduced crack propagation dynamics observed in field experiments, which employ the propagation saw test. The detailed microscopic analysis of weak layer stresses and bond breaking allowed us to define the crack tip location of closing crack faces, analyze its spatio-temporal characteristics and monitor the evolution of stress concentrations and the fracture process zone both in transient and steady-state regimes. Results highlight the occurrence of a steady state in crack speed and stress conditions for sufficiently long crack propagation distances (> 4 m). Crack propagation without external driving force except gravity is possible due to the local mixed-mode shear-compression stress nature at the crack tip induced by slab bending and weak layer volumetric collapse. Our result shed light into the microscopic origin of dynamic crack propagation in snow slab avalanche release that eventually will improve the evaluation of avalanche release sizes and thus hazard management and forecasting in mountainous regions.

scholarly journals Dynamic Fracture Analysis of Functional Gradient Material Coating Based on the Peridynamic Method

Coatings ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 62 ◽  
Author(s):  
Yu Zhang ◽  
Zhanqi Cheng ◽  
Hu Feng
Keyword(s):  
Elastic Modulus ◽  
Crack Propagation ◽  
Dynamic Fracture ◽  
Gradient Material ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Functional Gradient ◽  
Damage And Failure ◽  
Functional Gradient Material ◽  
Graded Material

Functional gradient materials (FGMs) have tremendous potential due to their characteristic advantage of asymptotic continuous variation of their properties. When an FGM is used as a coating material, damage and failure of the interface with the substrate component can be effectively inhibited. In order to study the dynamic crack propagation in FGM coatings, a new method, peridynamics (PD), was used in the present study to simulate dynamic fractures of FGM coatings bonded to a homogeneous substrate under dynamic loading. The bond-based PD theory was employed to study crack propagation and branching in the FGM coating. The influences of the coating gradient pattern, loading, and the geometry and size of the structure on crack curving and propagation under impact loading were investigated. The numerical results show that different forms of the elastic modulus of graded material, the geometry of the structure, and the loading conditions have considerate effects on crack propagation in FGM coatings, but a specific form of elastic modulus had a limited effect on the dynamic fracture of FGM coating.

scholarly journals New experimental techniques for dynamic crack localization

2009 ◽  
pp. 255-283
Author(s):  
David Grégoire ◽  
Hubert Maigre ◽  
Fabrice Morestin
Keyword(s):  
Crack Propagation ◽  
Crack Tip ◽  
Image Correlation ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Displacement Sensors ◽  
Optical Displacement ◽  
Propagation Parameters ◽  
Tip Position

The determination of relevant constitutive crack propagation laws under dynamic loading is a rather challenging operation. In dynamic impact cases, the variations of propagation parameters and exact crack positions are difficult to control. This paper focuses on different techniques for measuring accurate crack tip position histories in dynamic crack propagation experiments. Two different methods are considered: very accurate crack tip localization by optical displacement sensors is first described for transparent materials; then, an automatic method based on digital image correlation is presented for crack localization in all brittle materials whatever their opacity.

Fracture Behavior of X65 Q&T Seamless Pipeline Steel Under Different Strain Rates and Stress States

2020 ◽  
Author(s):  
Pratiwi Fudlailah ◽  
Marcelo Paredes
Keyword(s):  
Strain Rate ◽  
Dynamic Fracture ◽  
Wall Thickness ◽  
Fracture Behavior ◽  
Pipeline Steel ◽  
Economic Feasibility ◽  
Dynamic Crack ◽  
Strain Rates ◽  
Drop Weight ◽  
Stress States

Abstract Dynamic crack propagation in pressurized pipelines is usually investigated by means of lab-scale specimens due to its economic feasibility and material saving. More recently, new generation of pipeline steels have incredibly shown a combined fracture toughness and plastic strength capabilities with even more heavier wall thickness, for which current design standards and practice codes underpredict largely the actual material response under different strain rates. The Drop-Weight Tear Test (DWTT) is commonly used to characterize dynamic fracture behavior of pipeline steel and its numerical implementation with appropriate constitutive equations has become essential in the fundamental understanding of the interaction between fracture process and local stress-strain fields. In the present study, a X65 Q&T seamless pipeline steel is fully characterized under different strain rate levels and stress states for dynamic fracture initiation. A rate dependent phenomenological fracture criterion is proposed in the form of Modified Mohr-Coulomb (MMC) fracture model coupling with a multiplicative decomposition of the hardening law to describe strain rate effect on post-necking behavior. The model implementation is then validated through a drop-weight tearing analysis on standard and non-standard specimen configurations including different wall thickness.

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